All‐metallic Zn=Zn double‐π bonded octahedral Zn 2 M 4 (M=Li, Na) clusters with negative oxidation state of Zinc

Zn=Zn double bonded-especially double-pi bonded-systems are scarce due to strong Coulomb repulsion caused by the Zn atom's internally crowded d electrons and very high energy of the virtual pi orbitals in Zn2 fragments. It is also rare for Zn atoms to exhibit negative oxidation states within reported Zn-Zn bonded complexes. Herein, we report Zn=Zn double-pi bonded octahedral clusters Zn2 M4 (M=Li, Na) bridged by four alkali metal ligands, in which the central Zn atom is in a negative oxidation state. Especially in D4h -Zn2 Na4 , the natural population analysis shows that the charge of the Zn atom reaches up to -0.89 |e| (-1.11 |e| for AIM charge). Although this cooperation inevitably increases the repulsion between two Zn atoms, the introduction of the s(1) -type ligands results in occupation of degenerated pi orbitals and the electrons being delocalized over the whole octahedral framework as well, in turn stabilizing the octahedral molecular structure. This study demonstrates that maintaining the degeneracy of the pi orbitals and introducing electrons from equatorial plane are effective means to construct double-pi bonds between transitional metals.